Triangular based offshore platform



Jan. 9, 1968 F1 led June -17, 1965 w; F- MANNING 3,362,170

TRIANGULAR BASED OFFSHORE PLATFORM 5 Sheets-Sheet 1 4 III; I, II I I IIIIIIIIIIIIIH,H'IIIIIIIII I h/ in,

kl, AL 32 Y a M 20 in J .4%: I2 Her INVENTOR WILLIAM F. MANNING Jan. 9,1968 w. F. MANNING 3,352,170

TRIANGULAR BASED OFFSHORE PLATFORM 5 Sheets$heet 2 Filed June 17, 1965WILLIAM F. MANNING BY cued/w d Jan. 9, 1968 w. I-. MANNING 3,362,170

TRIANGULAR BASED OFFSHORE, PLATFORM I Filed June 17, 1966 3 Sheets-Sheet3 II I III TIIII IIIIIIIIIIIIIIIIIIIIIIITI rm m l IllllI/IIIIIIIIIII F06Ill? I/ -\l llllllllll'ljlll IIIIIIIIIIIII!lI/l/IIIITT F06 IIZ INVENTORWILLIAM F. MANNING BY W -F United States Patent Ofitice 3,362,170Patented Jan. 9, 1968 ABSTRACT OF THE DISCLOSURE This specificationdiscloses a triangular drilling and/ or production templet, and methodsfor installing the templet for drilling a subaqueous well and forcompleting, from a surface structure, an already drilled wellterminating in an underwater stubbed-oif conductor pipe. The templet hasa vertical leg and a pair of fixedly angled legs forming a triangularbase at the marine bottom, and converging upwardly. A buoyancy tank isfixed on the vertical leg near the marine bottom. An above-surface deckis mounted on the upper end of the templet. The templet legs areanchored against axial tension and compression forces by piles extendingtherethrough into the formations underlying the marine bottom. One ormore wells are drilled and/ or completed through the vertical leg whichmay be a single caisson or two or more rigidly connected parallelcaissons.

This invention relates to a compact marine platform to be erected at anoffshore submerged or subaqueous well site. More particularly, thisinvention relates to a prefabricated marine drilling and/or productionplatform having a hollow vertical support leg which functions to guide adrill string into the ocean bottom or conduct oil or gas from acompleted well.

Present developments in the offshore oil industry find exploration andproduction efforts being extended to areas of extremely deep andunprotected water. For example, drilling in waters of 600 feet is now areality and the exploration of the continental slope, out beyond thecontinental shelf, in depths of 1500 feet is close at hand. Differentdepths provide different problems and types of equipment required. Inshallow Water, a submerged barge appears the most practical. Up to 300feet of water, the rigid, bottom-supported structure has been shown tobe the most feasible with the prefabricated templet being the leastexpensive, and the jack-up rig the most versatile. In depths of over 300feet, the transparent, or semisubmersible, floating platform is nowconsidered the most desirable by many, while the ship-shape vessel stillcompetes where storms are not violent or continuous.

In the midrange of 100-300 feet of water, where a great deal of activityis centered at this time, there is the most overlap in drillingstructures used. The jack up platforms provide a motionless deck withpositive continuous location of the hole and depth versatility while theship-shape provides the most mobility, and the transparent floatingplatform gives a compromise between the other two. However, one of theproblems with jack-up platforms is that with the legs jacked up out ofthe water, above the platform, for towing, it is unstable in heavy seas.The most pressing problems with floating vessels are keeping them onlocation and minimizing pitch, roll, and heave.

For drilling in the above-designated midrange depths, it is not alwayseconomical to employ a floating vessel which may rent for as much as$12,000 a day, and therefore a light, compact templet would be desirablefor drilling. Such a structure should be little more than bracing for ariser or caisson between a point above the surface of the body of waterand a point beneaththe bottom thereof and support for a drilling deck.The templet structure should furthermore be capable of being floated tothe site and be reasonably stable in the floating state in rough seaswhile under tow.

For production, in the midrange, the floating designs are impractical,and of the surface equipment under consideration, only bottom-supportedstructures are seriously contemplated. Due to the fact that a productionplatform does not have to be especially mobile, the primaryconsideration is cost. When a platform is to be anchored over a well foryears at a time, it becomes incumbent on the designer to devise astructure that will be of minimum cost with sufficient strength towithstand the wind and wave loadings contemplated. The type of structurethat best meets these design criteria would be a bare riser and bracingtherefor, as described in the preceding paragraph.

Accordingly, it is an object of this invention to provide a relativelylightweight bottom-supported marine platform.

It is another object of this invention to provide a bottom-supportedmarine platform consisting essentially ofv a supported conductor orriser pipe extending from a.

point above the surface of a body of water to a point beneath the bottomof the body of water. It is a further object of the invention to providea bottom-supported platform which is stable While being towed to asubmerged site.

Other objects and advantages of this invention will be readily apparentfrom the following description when read in conjunction with theaccompanying drawings which illustrate useful embodiments in accordancewith this invention.

In the drawings:

FIGURE 1 is a perspective view of a bottom-supported templet structureof the invention with a drilling platform aflixed to the upper endthereof, above the surface of the water;

FIGURE 2 is a perspective view of a similar bottom supported templetstructure with a production platform affixed to the upper end thereof,above the surface of the water;

FIGURES 35 illustrate in diagrammatic representations the sequentialsteps required for installing a production templet, as shown in FIGURE2, over a previously drilled well.

In accordance with the present invention, the marine drilling and/orproduction templet comprises a vertical working leg and a pair offixedly angled support legs, one at each of three corners, to form astructure having a substantially triangular cross section. The legs arewidely spaced at the lower end of the structure to form a broad base andconverge at the upper end, at approximately the surface of the water.The legs are also interconnected by braces appropriately spaced atintervals along the length of the templet structure. All three legs areanchored by piles driven therethrough into the formations underlying themarine bottom, the legs being rigidly connected to the piles bycementing and/ or welding. The vertical working leg is composed of oneor more hollow caissons connected to a point within the formationsunderlying the marine bottom of the body of water by a hollow pile, eachcaisson-pile combination serving as a conductor pipe, or riser, forpermitting a subaqueous well to be drilled from a deck above the templetstructure through each caisson. A cylindrical buoyant tank is fixed tothe lower end of the vertical working leg to relieve some of the load onthe vertical leg. The axis of the cylindrical buoyant tank is parallelto the axes of the caissons making up the working leg. For a compactarrangement the vertical working leg can extend centrally through thebuoyant tank. Each of the support legs is also hollow and can beutilized for production storage. To float the templet to the site, theopen ends of the legs are capped, forming large buoyant tanks. Thecapping of the hollow legs and the later controlled flooding thereof forproperly aligning 3 the templet is old in the art and is not a part ofthe present invention.

When using a templet structure of the type herein disclosed solely as aproduction platform, after a subaqueous well has been already drilledfrom a mobile platform, the subaqueous well is left with a stubbed-offconductor pipe extending up out of the subaqueous well, and strongenough to function as a structural piling. The templet structure istowed to the site in a buoyant condition, the caps are removed from thelower ends of the legs and then portions of the templet are sequentiallyflooded until the templet is submerged, but above the bottom, with thevertical working leg correctly oriented. The templet is then completelyflooded by removing the caps from the upper ends of the legs as thetemplet is lowered with the vertical leg telescoping over the upwardlyextending stubbed-off conductor pipe. Piles are driven through the othertwo legs to anchor them in place. Cement is then injected between eachof the fixedly angled support legs and the respective enclosed pile aswell as between the vertical working leg and the mated conductor pipe,to cement the three legs in place.

Referring to the drawings, FIGURE 1 illustrates a rigid drillingplatform consisting of a triangular templet structure 12 and a drillingdeck 14. The drilling platform 10 has a vertical leg 16 formed by a pairof rigidly connected hollow caissons 18 surrounded at their lower endsby a buoyant cylindrical tank 20, and a pair of upwardly convergingsupport legs 22. The legs 16 and 22 are all interconnected by spacedhorizontal braces 24 and triangulated for strength by auxiliary braces26 between each level of horizontal braces 24. The vertical leg 16 aloneextends through the deck 14 atop the templet 12, and a drilling rig 28is centrally located thereover for drilling through one of the hollowcaissons 18. The fixedly angled support legs 22 terminate just below thedeck 14 where they provide a base for the support braces 30 of the deck14. To appreciate the size of such a structure, it is calculated that inthree hundred feet of water the support legs 22 would be sixty-inchdiameter tubes while the caissons 18 would be thirty inches in diameter.

The lower end of each of the legs 22 rests on the bottom 34 and isanchored therein by a pile 32 which is driven down into the formationsunderlying the marine bottom 34 through the hollow leg 22 before thedrilling deck 14 is fixed thereon. A hollow pile 36 is driven throughthe bottom 34 through each of the caissons 18, making up the verticalleg 16. Grout or any other suitable cementing material is injectedbetween the piles 32 and 36, and the legs 22 and caissons 18 of leg 16,respectively, to cement the piles to the legs 22 and 16. Alternativelythe piles 36 and 32, respectively, can be welded within the hollow legs22 and caissons 18 above the surface of the water at the upper end ofthe templet structure 12. The piles 32 in legs 22 anchor the legs inplace in the formation underlying the marine bottom 34 of the body ofwater while the piles 36 serve the double function of anchoring the leg16 and providing water-tight extensions of the caissons 18 for guidingdrill pipe into the formations underlying the marine bottom 34 whiledrilling a subaqueous well.

The drilling rig 28 is set in place over one of the caissons 18 fordrilling a subaqueous well therethrough. After the well has been drilledto the desired depth, the rig can be moved a short distance across thedeck 14 to be centered over the other caisson 18 and the drillingprocedure repeated. Since the structure 10 is of the permanent type, itcan be left in place after the drilling has been successfully completed,and then used as a production platform. The drilling rig would then beremoved and a wellhead structure commonly termed as Christmas tree (notshown) would be installed on the deck 14 over each caisson 18.

FIGURE 2 illustrates a templet 12 supporting a production deck 14' overa subaqueous well 38. The platform 10 is similar in concept to thedrilling platform 10 of FIGURE 1, having a hollow cylindrical verticalleg 16' with a buoyant cylindrical tank 20' concentrically aifixedthereon, and a pair of fixedly angled support legs 22. In theillustrated embodiment the leg 16' is itself the caisson, although theleg 16 could be comprised of several rigidly connected parallel caissonsas illustrated in FIGURE 1 and described previously. While the supportlegs 22' are anchored, as in the first described embodiment, by piles32' driven therethrough into the formations underlying the marine bottomof the body of water, the vertical leg 16' is telescoped over, or into,an existing stubbed-oif conductor pipe 36 extending upwardly from adrilled subaqueous well in the bottom 34. The production platform 10 ofFIGURE 2 is of a lighter and simpler construction than the drillingplatform 10 of FIGURE 1 since it is never required to support a drillingrig. The production deck 14' need not be fixed to the templet structure12 by an extensive bracing structure as shown in FIGURE 1. Instead itcan be mounted solely on the upper end of the vertical leg 16', the onlyportion of the templet structure 12' breaking the surface, thuspermitting the smallest possible frontal area to be acted on by waveforces in the turbulent surface water zone. As shown, the productiondeck 14 Consists of a lower floor 40 and an upper floor 44. The leg 16extends through the lower floor 40, ending in a Christmas tree 42. Theupper floor 44 is an unobstructed fiat area where a servicing helicoptercan land. Oil and/or gas may be pumped up through the leg 16 from thewell 38 to equipment on the production deck to pressure relieve theproduced fluid as well as to separate it into gaseous and liquidcomponents. The products can then be stored in the hollow legs 22.

FIGURES 3-5 graphically illustrate the installation procedure forcompleting a stubbed-otf subaqueous well to the surface by utilizing theproduction platform 10. In FIGURE 3 the templet 12' is shown being towedto the subaqueous well site by a ship 46. As previously described, thetemplet structure 10' can be made buoyant by capping the legs 16 and 22'prior to immersion. The templet 14 lies in the water on a side with thetwo support legs 22' floating on the surface of the water and thevertical leg 16' in the air between them. Since the vertical leg 16' iscentered between the two support legs 22 and is not relatively high inthe air, the templet 12' is fairly stable while being towed.

When the templet has been towed to a position adjacent a mobile drillingplatform 48, after the drill pipe has been removed from the finishedwell 52, the capped ends (not shown) are broken away from the lower endsof the legs 16' and 22, and the templet legs 16 and 22 flood, causingthe templet 12' to sink. By connecting the upper end of leg 16 to thedrilling derrick 50 on the mobile rig 4S centered over the well 52, andholding the other legs 22' by the tow ship 46 to obtain correctorientation, the templet 12' can be held with the leg 16' in a verticalposition above the bottom 34. The caps (not shown) covering the upperends of the legs 16' and 22' can then be removed to complete theflooding. The templet 12' is lowered to telescope the lower end of thevertical leg 16 into the upper end of the stubbed-off conductor pipe 38.Piles 32' are then driven down through legs 22' from the surface intothe formations underlying the marine bottom 34 and the piles 32' and thestubbedoff conductor pipe 38 are cemented to their respective legs 22'and 16, respectively.

The production deck 14' is now mounted atop the bottom-supported templetto form a permanent production structure. The Christmas tree 42 is fixedover the leg 16' (if the leg 16' consists of only one caisson, or one isfixed over each of the caissons forming the leg 16 if the leg 16consists of more than one caisson, whichever is the case). The mobiledrilling rig 48 can then be towed away to drill a subaqueous well atanother site and the instant well is able to produce oil above thesurface of the water.

The drilling platform (FIGURE 1) is installed in a similar manner tothat described above for the production platform 10. The templet 12 isalso towed to the site in a buoyant condition. However, in most casesthe templet 12 can be flooded and set on the site without a derrickoverhead to guide it. The location of the working leg is not as criticalwhen a new hole is going to be drilled as when the leg must be stabbedover a conductor pipe extending upwardly from an already drilled well.Another slight variation in the installation procedure is the driving ofa pile 36 down through each of the caissons 18 forming the working leg16 as well as driving piles 32 down through the support legs 22.

Although the present invention has been described in connection withdetails of specific embodiments thereof, it is to be understood thatsuch details are not intended to limit the scope of the invention. Theterms and expressions employed are used in a descriptive and not alimiting sense and there is no intention of excluding such equivalents,in the invention described, as fall within the scope of the claims. Nowhaving described the apparatus and method herein disclosed, referenceshould be had to the claims which follow.

What is claimed is:

1. A prefabricated bottom-supported templet structure for use in a bodyof water to support equipment above the surface of the body of water andto provide at least one watertight vertical passage from said equipmentabove the surface of said body of water to a point within the formationsunderlying the marine bottom comprising a vertical leg and only twohollow fixedly angled legs for supporting, in part, said vertical leg;said fixedly angled legs being fixedly positioned to form a structurehaving a substantially triangular cross section; said equipment beinglocated substantially directly over the upper end of said vertical leg;a buoyant tank fixed to said vertical leg whereby the portion of theweight of said above-surface equipment on the vertical leg will belessened, preventing said vertical leg from being driven further intothe forma tions underlying the marine bottom than said angled legs priorto said templet structure being firmly anchored .in the formationsunderlying the marine bottom; means for sealably connecting andanchoring the lower end of said vertical leg in the formationsunderlying the marine bottom, said sealably connecting and anchoringmeans comprising the upper portion of a subaqueous well formed in theunderlying formations and extending to producible subaqueous mineraldeposits; said support legs being spaced apart at said marine bottom,converging upwardly toward said vertical leg, and terminating at a pointadjacent said surface of said body of water; and means for anchoringeach of said support legs within the formations underlying said marinebottom against axial compression and tension forces.

2. The prefabricated bottom-supported templet structure of claim 1wherein said equipment comprises a deck mounted on said templet so as tobe above the surface of the body of water in which said templet islocated, said vertical leg comprising at least one hollow caissonextending through said deck whereby said watertight vertical passageextends from a point above said deck into the formations underlying saidmarine bottom.

3. The prefabricated bottom-supported templet structure of claim 1wherein said vertical leg comprises two parallel hollow caissons rigidlyfixed together, forming a pair of separate watertight passages fromrespective points above the surface of said body of water to respectivepoints within formations underlying said marine bottom and formingextensions of su-baqueous wells in the underlying formations.

4. The prefabricated bottom-supported templet structure of claim 1wherein said means for sealably connecting and anchoring said caissoninto said formations underlying said marine bottom is a hollow piledriven into said formations through said caisson and fixedly cementedtherein whereby a drilling rig located directly over said vertical legon said deck above said surface of said body of Water can drill asubaqueous well through said vertical leg.

5. The prefabricated bottom-supported templet structure of claim 1wherein said buoyant tank is fixed to the lower end of said vertical legwhereby said buoyant tank is located downward of the turbulent surfacewater zone.

6. The prefabricated bottom-supported templet of claim 5 wherein saidbuoyant tank is cylindrical and the axis thereof is parallel to the axisof said vertical leg when fixed thereto.

7. The prefabricated bottom-supported templet of claim 6 wherein saidvertical leg extends through said buoyant tank.

8. The prefabricated bottom-supported templet of claim 2 wherein saidfixedly angled legs terminate below said surface of said body of waterand only said vertical leg extends above said surface of said body ofWater.

9. A method for installing an olfshore production platform over a fixedstubbed-off conductor pipe extending up vertically from a previouslydrilled subaqueous well at a submerged site, wherein said platformcomprises the templet structure of claim 2, including the followingsteps:

(a) flooding said hollow legs Olf said templet to submerge said templetat said site;

(b) positioning said templet during flooding to orient said verticalleg;

(c) guiding said vertical leg into telescoping relationship 'with saidfixed upwardly extending conductor w ((1) driving piles into saidformations underlying said marine bottom through each of said fixedlyangled legs, from the upper ends thereof, to anchor said piles;

(e) fixing each of said piles rigidly within the respective fixedlyangled leg to anchor said respective fixed angled leg with respect tosaid marine bottom;

(f) anchoring said vertical leg by a watertight connection between saidvertical leg and said conductor pipe to form a continuous passagethrough said leg and said conductor pipe into said drilled well wherebysaid well can be completed so that oil and/or gas may be producedthrough said vertical leg; and

(g) mounting a working deck on said templet above said surface of saidbody of water.

References Cited UNITED STATES PATENTS 2,248,051 7/1941 Armstrong 6146.52,637,978 5/1953 Evans 6146 2,901,890 9/1959 Hutchison 6146 2,906,5009/1959 Knapp 6l-46.5 X 3,209,544 10/1965 Borrmann 6146'.5

JACOB SHAPIRO, Primary Examiner. DAVID J. WILLIAMOWSKY, Ex miner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,362,170 January 9, 1968 William F. Manning It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 3, line 55, for "formation" read formations column 6, line 5, forthe claim reference numeral "1" read 2 Signed and sealed this 25th dayof February 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissionerof Patents

